G major scale has the same tones as C major scale, except for F, which now becomes F#.

D major scale has the same tones as G major scale, except for C, which now becomes C#. Its two sharps are F# and C#.

A major scale has the same tones as D major scale, except for G, and so on…

In other words, F is the first tone that is made sharp, C is the second tone that is made sharp, G the third, and so on clockwise around the circle.

You can also find the flats using the same picture but now we start on B and work backwards.

The order of flats in the key signature is: B – E – A – D – G – C – F

Let’s apply it:

C major scale has no flats.

F major scale has the same tones as C major scale, except for B, which now becomes Bb.

Bb major scale has the same tones as F major scale, except for E, which now becomes Eb. Its two flats are Bb and Eb.

Eb major scale has the same tones as Bb major scale, except for A, and so on…

Did you notice that each time you take the next step, which tone changes?

If we go clockwise, for example from the key of C to the key of G, the tone that changes is F, which becomes F#. F is directly to the left of C. So you can look to the left (or rather, counterclockwise) of your starting key to see which tone has to be raised.

If we go counterclockwise, it works slight differently: the tone to the left is now the one that has changed. Say we go from the key of C to the key of F. One step left from F is Bb, which means the B tone was flattened to become Bb.

So you can look in the circle to see which tone you have to change.

You can also remember which scale step to raise or lower:

Clockwise, raise the 4th note from the scale. From C to G, we first find the 4th note from the C major scale, which is F. We raise F to get F#. The note that has changed will also be the 7th note of the new scale.

Counterclockwise, lower the 7th note from the scale. From C to G, the 7th note from the C major scale is B. We lower B to get Bb. The note that has changed will also be the 4th note of the new scale.

What if you quickly want to know which tones need to be sharpened for a particular key signature? Look up the key in the circle, let’s say the key of A. Go counterclockwise one step (we skip this one). Then all the tones counterclockwise back to F must be sharpened. So in this case we skip D (this one doesn’t change) and sharpen G, C and F.

Getting the flats is a little harder. You move counterclockwise one step from your key signature and then go back clockwise again until you reach Bb. So in the key of Ab, we first go to Db and then back to Bb: Ab, Eb, Bb. So the key of Ab has four flats: Db, Ab, Eb, Bb. A little tricky, this one.

There is another method. Go directly across the circle from your key signature, then count clockwise to B and flat all these notes. From Ab across the circle gets us at D, then clockwise we meet A, E and finally B. We flatten these notes to find the four flats: Db, Ab, Eb, Bb. Still a little convoluted, but hey, it’s possible!

If you know which notes are flattened, how do you determine the key? The name of the key is the second-to-last flat in the list. For example, in the picture below the flats are: Bb – Eb – Ab – Db – Gb. The second-to-last is Db, so the key must be the key of Db major.

Or you could just count the number of flats and go counterclockwise that many steps in the circle, starting from the top.

For sharps it is even easier: Take the last sharp in the list and go up a half-step to find the name of the key. In the picture below the sharps are: F# – C# – G#. To find the key, raise G# by a half-step, which results in: the key of A major.

Of course, here you can also count the number of sharps starting from the top, but this time we go clockwise.

It is easy to see that the circle goes F – C – G – D – A – E – B clockwise. These are all names without sharps or flats. But because B is enharmonically equivalent with Cb, it continues Cb – Gb – Db – Ab – Eb – Bb clockwise. Do you notice, with the exception of F, that this is the same as the first list but simply with added flats?

To find the notes in the current key, read the five notes clockwise and the one note counterclockwise. You can also simply go one position counterclockwise and then read seven notes going clockwise.

So from G we go left once to find C, then we go six times clockwise to find G, D, A, E, B and F#. Put these in alphabetical order and you have the notes from the key of G.

This works for all keys, although sometimes you’ll have to turn flats into sharps for it to make sense. Applying this formula to the key of D would give you G, D, E, A, B, F#, Db but you should obviously turn that Db into a C#.

Phew! That’s a lot of crazy things you can do with the circle and key signatures.